For the purposes of this invention, conveyors are conveyor belts, bucket conveyors, hydraulic screws and hydraulic turbines, etc. with which material to be conveyed is only to be transported in one direction. When this conveyor comes to a standstill, it must thereby be ensured that any material still in, at or on the conveyor does not move the conveyor back opposite the usual direction of conveyance due to the force of gravity.
For this purpose, it is known, for example, to provide freewheels as return locks on drives of conveyor belts. They prevent a drive shaft for the conveyor belt from being able to rotate opposite a preset direction of rotation, for example, during a power failure of a drive motor.
However, nowadays, freewheels of this type are very expensive components which also increase over-proportionately in price with their size.
From this point of view, an arrangement of the freewheel on the drive shaft would be desirable since it runs the quickest. However, this is not possible for reasons of accessibility (maintenance, repair), in particular in tapered spur-gear systems.
For this reason, in a gear arranged between drive motor and the actual conveyor belt drive shaft, it is common to place the freewheel on an intermediate shaft between drive axis and output axis instead of on the output axis. In intermediate shafts of this type which are situated between quickly running drive shaft and slowly rotating output shaft, the torque which is to be maintained in the case of a stoppage and is inversely proportional to the rotational speed is less than the output shaft. Accordingly, a smaller freewheel can be selected.
However, it was shown that three-speed gears are often used for this reason as gears alone instead of two-speed gears, so that the speed of the gear train which supports the freewheel can run especially quickly, i.e. with a low torque, in order to be able to thus use an inexpensive freewheel. However, this also results in an additional step in the output flow, which results in an unintentional power loss. In particular, with a power loss of this kind, a larger housing must be provided in turn, so that the power loss produced can be diverted.
Accordingly, the object of the present invention is to further develop a gear for a conveyor as described above such that a smaller and thus more economical freewheel can be used without unnecessarily increasing the cost of the actual gear line by providing additional intermediate steps.
According to the invention, this object is solved in that there is at least one second gear step, which only drives the freewheel, between the freewheel and the elements transmitting the torque between drive and output shaft during operation of the gear.